1. Field of the Invention
This invention relates to monitoring and controlling the temperature of an integrated circuit.
2. Description of Related Art
An integrated circuit operating at a constant fixed level of activity has an equilibrium temperature which is eventually reached. At equilibrium, the heat lost to the surroundings of the circuit on average equals the heat generated by the circuit. The temperature, therefore remains roughly constant. Unfortunately, the equilibrium temperature of an integrated circuit is often above the safe operating temperature and a cooling scheme is needed.
Many high performance microprocessor systems experience excessive heat buildup in the central processing units (CPU) due to high power dissipation. Conventional cooling schemes for these systems use either a cooling fan or a large heat sink. Cooling fans move air past the integrated circuits and thereby increase the heat loss from the integrated circuits to the surroundings. This lowers the equilibrium temperature. However, cooling fans are large (compared to the scale of an integrated circuit), consume power, and can be noisy. Heat sinks are also large, in addition to being expensive and less effective. In portable computers where size and power consumption are critical, neither fans nor heat sinks are practical.
The temperature of a CMOS integrated circuit depends on the power used by the integrated circuit which is proportional to the clock speed or frequency of operation of the integrated circuit. Prior art power control schemes can change clock speed and therefore change circuit temperature. However, existing power control schemes are aimed at preserving battery power in devices such as portable computers and not at monitoring integrated circuit temperature. Any effect of such power saving circuitry on temperature is coincidental and ineffective at limiting worse case heat buildup.